This invention relates to an image forming apparatus which forms an image by superposing an image receiving sheet on a light receiving sheet comprising a photosensitive film on which a selectively hardened image is formed.
A light receiving sheet which may be used for such an image forming apparatus has been disclosed, for example, in Japanese Patent Publication Tokkai 58-88739. Such a sheet is formed by coating the surface of a flexible base material with pressurerupturable microcapsules encapsulating a colorless dye and a photopolymerizable substance as an example of substance which hardens by exposure to light and a selectively hardened image can be formed on such a sheet by exposing it to an image carrying beam of light. In other words, if an image carrying beam of light such as a reflected beam of light from an original document to be copied is made incident on such a light receiving sheet, only those of the microcapsules exposed to light are hardened and there results as a whole a pattern, or image, formed by selectively hardened microcapsules. In order to form a visible image from such a pattern, or image, formed on the light receiving sheet, an image receiving sheet coated with a developing agent is superposed on the image carrying sheet and they are pressed together. As a result of this compression process, those of the microcapsules which were not hardened are ruptured and the colorless dye encapsulated therein flows out, causing a chromogenic reaction with the developing agent with which the surface of the image receiving sheet is coated and thereby forming a visible image of the original to be copied.
When a light receiving sheet is used in connection with such an image forming apparatus, it is extremely important to prevent external light from being made incident thereon and external force from being applied thereon before it reaches the so-called exposure point where it is intentionally exposed to the image carrying bean of light reflected from an original. The reason for the latter is that the microcapsules may otherwise rupture by a carelessly applied external force. One method of protecting the unused light receiving sheet from external light and force is to prepare it in the form of a roll and preliminarily set such a roll inside a container and to wind it up after the image formed thereon has been transferred to an image receiving sheet as described above. One advantage of this method is that the light receiving sheet can be wrapped directly around a drum-like cylindrical structure on which the aforementioned exposure point is defined such that the light receiving sheet can be supplied and removed by the rotation of this cylindrical structure and hence that feed rollers and guide rollers of the kind required if the sheets are to be supplied from a tray can be dispensed with. Moreover, since the used sheets can be taken up and stored internally, images containing confidential information, for example, can be more easily controlled and the used sheets can be removed more expediently.
After two sheets are superposed one on top of the other and pressed together to transfer an image from one to the other, they must be separated from each other. A means for this purpose (hereinafter generally referred to as a sheet separator) is generally disposed behind the transfer position where the sheets are pressed together and the image is transferred from one to the other. If the image forming apparatus is adapted to wind up the used portions of the light receiving sheet, the front end (the leader section) of the originally rolled sheet is preliminarily wound around a take-up shaft. If the sheet separator is disposed at a fixed position in such an apparatus, however, the process of initially attaching the leader section of the light receiving sheet to the take-up shaft becomes difficult to perform. If the apparatus is of the kind which causes the leader section of the light receiving sheet to be automatically pulled out of its container (cartridge) after it is set inside the apparatus and passed through the transfer position to the take-up shaft, in particular, the sheet separator at a fixed position tends to interfere with the forward movement of the leader section and to cause a jam.